Various different types of devices are commercially available which can be used to puncture or pierce a patient's skin. These include devices, such as those disclosed in U.S. Pat. Nos. 5,133,730 and 5,755,733, which are designed to prick the patient skin, for example a finger tip, as well as devices that are configured to produce an incision of a uniform length and depth in the skin.
As will be appreciated, devices which can produce a precisely controlled uniform incision can be used in conjunction with a variety of different medical tests or procedures including, for example, bleed time tests and for drawing blood for subsequent collection. More particularly, one important use for such incision devices is to produce an incision in the skin of an infant, generally in the heel, so as to enable blood to be collected for tests, such as metabolic screening tests.
Available incision devices generally utilize a spring arrangement to produce the energy necessary to drive the cutting blade through the patient's skin. With these devices, such as for example the device disclosed in U.S. Pat. No. 4,643,189, a spring is typically assembled into the device in a biased condition so that it is storing the energy which will be used to drive the cutting blade when the device is triggered. The biased spring, however, adversely effects the stability of the device. In particular, the biased spring can make accidental or premature triggering or discharge of the device, which can occur simply through inadvertent touching of the trigger, much more likely. Moreover, having the spring in a biased condition also places many of the other components of the device under stress resulting in an overall reduction in the shelf-life of the device.
Since it is generally preferable to design these devices so that they are disposable after a single use, minimizing material, manufacturing and assembly costs is always an important consideration for producing a commercially viable product. However, assembling the spring in a biased condition makes the device more difficult to manufacture, sometimes requiring the provision of special jigs, resulting in increased manufacturing and assembly costs for the device. Additionally, if provisions, such as safety caps, are included to help prevent premature firing or discharge of the device, it can further increase the material, manufacturing and assembly costs.